Spray painting, in which a liquid paint is first atomized and then applied to the car body surface to form a uniform thin liquid film still remains the basic method of applying the intermediate and final paint coats. Against the backdrop, the automated paint systems used to apply the intermediate and final coats have been switched in many cases to electrostatic rotary atomizers. With the rotary atomizer method, liquid paint is supplied from the rear to the center of a bell cup and is discharged from the bell edge by the centrifugal force created by high speed rotation of the bell. The spray pattern is formed by the shaping air supplied from the rear. The trajectories of large-size particles having greater mass are less apt to bend, while those of small-size particles on the other hand, bend considerably with the result that they tend to be concentrated in the center of the spray pattern. Whether these particles are transferred or not has a large effect on transfer efficiency. Overly large particles do not level out sufficiently on the painted surface and tend to become defects. Efforts have been made to optimize the painting conditions. However, the factors causing the formation of large-size particles have still not been analyzed fully. This paper presents the results of a paint atomization study that focused on the flow of the liquid paint film on the inner surface of the bell cup due to centrifugal force. It was decided to give the bell cup a convex shape on an experimental basis. The bell cup with a convexly curved inner shape showed the following features in comparison with the conventional bell cup used so far: 1. It achieves uniform atomization with a relatively narrow particle size distribution. 2. It provides a relatively smaller mean particle diameter, allowing the bell rotational speed to be reduced while still obtaining the same mean particle diameter as with a conventional bell atomizer. 3. Because the convex bell produces few large-size particles, it is easy to adjust the spray pattern, making it possible to attain higher transfer efficiency. 4. For the same reason, it is possible to achieve a paint film with excellent smoothness.


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    Title :

    Steady-state paint flow under high centrifugal force: atomization in spray painting


    Additional title:

    Stationäre Farbströmung unter hoher Zentrifugalkraft: Zerstäubung beim Spritzlackieren


    Contributors:
    Kazama, S. (author)

    Published in:

    JSAE Review ; 24 , 4 ; 489-494


    Publication date :

    2003


    Size :

    6 Seiten, 11 Bilder




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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